The present invention relates to a zoom lens, and in particular, relates to a zoom lens which is small in size with high picture quality and has a variable magnification range which sufficiently covers a normal photographing range, a camera which has such a zoom lens as a photographing optical system, and a portable information terminal device which has such a zoom lens as a photographing optical system of a camera function part.
The market for cameras used for security or the like has greatly increased, and there have been a broad range of requests. In particular, high picture quality and high variable magnification are always desired by users, and on which great emphasis is laid. Therefore, both high performance and high variable magnification are also requested for a zoom lens used as a photographing lens.
Here, in terms of high performance, resolution corresponding to at least a 1 mega-pixel to 5 mega-pixel image sensor is needed throughout an entire zoom range. Additionally, in terms of high variable magnification, approximately a 16× magnification is considered to be necessary.
In addition, so as to perform photographing even in darkness, it is desired that aberration be sufficiently corrected even in a near-infrared wavelength region.
Further, a wide-field angle is also desired, and a half-field angle at a short focal length end of a zoom lens is preferably equal to or more than 20 degrees.
Furthermore, a large diameter is also desired, an f-number at a short focal length (also referred to as wide angle) end is preferably less than or equal to 2.0.
As a conventional example of a zoom lens which includes, in order from an object side to an image side, a first lens group with a positive refractive power, a second lens group with a negative refractive power, a third lens group with a negative refractive power, and a fourth lens group with a positive refractive power, and in which the first lens group is constituted of, in order from the object side to the image side, a cemented lens of a negative lens and a positive lens, a positive lens, and a positive lens, and an anomalous dispersion glass is used in the first lens group, there are zoom lenses disclosed in Japanese Patent Application Publication Numbers 2003-262793, H08-005920, H06-289295, H08-082742, and the like.
In Japanese Patent Application Publication Numbers 2003-262793, H08-005920, H06-289295, H08-082742, no consideration for aberration correction in a near-infrared wavelength region is given.